My ds had a Mickey party and dd had a Minnie party, of course months after our trip and I had no supplies. Locally, unless you want to spend lots of money on plates etc, there wasn't much to choose from. I COULD not get a Mickey cookie cutter (I bought one last week!!) at the time, but was planning on making Mickey shaped sandwiches with it. On this past weekend, just to have fun, I made Mickey head shaped rice krispies with chocolate squiggled on top - you could make these ahead and wrap them up for the loot bags.
For the parties, I used any and all of the stuff I brought home from our trip to decorate - popcorn buckets, the disposable black plates in Mickey shape, etc. I just used red plates and napkins from the dollar store. I bought cheese nips and such (mice like cheese...), served cheese pizza etc. For my ds, he had a Mickey and Pluto party, so I made jello jigglers with a "dog cookie" cookie cutter. My mil is very talented and made embroidered Mickey badges for one party and personalized Minnie/Mickey door hangers for another. If you are heading to the park, you could pick up the snack mix with Mickey pretzels and crackers in it to serve at the party ($4 at WDW). There are also small sized boxes of character cookies for about 1-$1 to $1.50 at WDW I am sure you can get at DL that would be cheaper for the loot bags. You can also get the chocolate coins in mesh bags in the characters (not sure of exactness here - but around $3 for 10?) to split up for loot bags. I can't think of any smaller inexpensive things, other than the bags of Goofy candy you could open up and put into bags. There are lots of little things you could get, but you would be spending $5-6 on each item I think (I am thinking of personalized guest of honour badges and pins and such), depending on the age of the kids coming.
I also put a lot of work into theming my party favours for my kids and don't put in a lot of candy. I had bought lots of Disney stickers, note paper, pencils etc from my local dollar store in ours. For my dd I made Minnie skirts for the girls (got an awesome deal on fabric - couldn't resist) and glued black foam ears onto headbands for everyone (of course I added the bow for the girls). For the boys I bought black belts (actually dog collars) from the dollar store and attached black cable wire to them for Mickey tails for the boys.
HTH!